Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$172.35	8.439%	$186.8946	$186.89	$186.90	$186.90
Purchase #2	$42.68	6.827%	$45.5938	$45.59	$45.60	$45.60
Purchase #3	$234.78	4.467%	$245.2676	$245.27	$245.25	$245.30
Purchase #4	$122.45	4.395%	$127.8317	$127.83	$127.85	$127.80
Purchase #5	$133.82	13.274%	$151.5833	$151.58	$151.60	$151.60
Purchase #6	$84.77	3.655%	$87.8683	$87.87	$87.85	$87.90
Purchase #7	$208.93	4.282%	$217.8764	$217.88	$217.90	$217.90
7 purchase totals =	$999.78		$1,062.9157	$1,062.91	$1,062.95	$1,063.00